Darwin's Dangerous Idea by Daniel C. Dennett

Author:Daniel C. Dennett [Dennett, Daniel C.]
Language: eng
Format: epub
Published: 2011-10-14T15:49:33+00:00

270 BULLY FOR BRONTOSAURUS

The Spandrel's Thumb 271

should expand our reverse-engineering perspective back onto the processes of R and D, and embryological development, instead of focusing "exclusively on immediate adaptation to local conditions." That, after all, is one of the main lessons of the last two chapters, and Gould and Lewontin could share the credit for drawing it to the attention of evolutionists. But almost everything else that Gould and Lewontin have said militates against this interpretation; they mean to oppose adaptationism, not enlarge it. They call for a "pluralism" in evolutionary biology of which adaptationism is to be just one element, its influence diminished by the other elements, if not utterly suppressed.

The spandrels of San Marco, we are told, "are necessary architectural byproducts of mounting a dome on rounded arches." In what sense necessary?

The standard assumption among biologists I have asked is that this is somehow a geometric necessity, and hence has nothing whatever to do with adaptationist cost-benefit calculations, since there is simply no choice to be made! As Gould and Lewontin (p. 161) put it, "Spandrels must exist once a blueprint specifies that a dome shall rest on rounded arches." But is that true?

It might appear at first as if there were no alternatives to smooth, tapering triangular surfaces in between the dome and the four rounded arches, but there are in fact indefinitely many ways that those spaces could be filled with masonry, all of them about equal in structural soundness and ease of building. Here is the San Marco scheme (on the left) and two variations. The variations are both, in a word, ugly (I deliberately made them so), but that does not make them impossible.

Here there is a terminological confusion that seriously impedes discus-FIGURE 10.2. The ceiling of King's

College Chapel.

"constraint"—as if the discovery of such constraints weren't an integral part of (good) adaptationist reasoning, as I have argued in the last two chapters.

Now, perhaps we should stop right here and consider the possibility that Gould and Lewontin have been massively misunderstood, thanks to the misfiring rhetoric of this opening passage, rhetoric which they even correct somewhat, in the last sentence quoted above. Perhaps what Gould and Lewontin showed, in 1979, is that we must all be better adaptationists; we FlGURE 10.3

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